GSK3B and Alzheimer disease: The majority of tau phosphorylation occurs at the residues located outside of the MBD and this is considered to be an early pathologic event in AD.[20] Using an in vitro phosphorylation reaction and MS analysis, we identified two phosphorylation sites, Ser324 and Ser356, in tau‐AC; both sites contained the Lys‐Ile‐Gly‐Ser motif in the R3 and R4 repeats, respectively (Figure S2A, Supporting Information).[3] Unexpectedly, tau‐AC, which was phosphorylated with recombinant GSK3β, showed considerably less self‐aggregation than intact tau‐AC (Figure S2B, Supporting Information).